ORP & Ph sensing plumbing question

[Rick Sass]

I'm going to be installing a Sense & Dispense system that has a SWG, a cartridge filter and Goldline ProLogic controller. My question is regarding the plumbing of the effluent tubing of the probe cell to the pool supply/suction side of the exisitng pool plumbing. The installation manual shows the effluent side of the probe cell installed before the pool pump. My existing pool plumbing will not allow me to install the flex tubing for the effluent port before the pump (I have a check valve and then valve actuators immediately before the pool pump and I do not want to replumb the suction side of the pool plumbing); I can however install the effluent tubing after the pump and before the filter.

Is the reasoning for installing the effluent tubing before the pump (suction side) is that the pump suction will pull/suck the water from the probe cell and then be filled with pool water from the influent tubing on the return (supply) side?

If I install the effluent tubing between the pump and filter does that mean that the probes will not be testing/monitoring a constantly changing flow of pool water but rather a stagnant pool sample?

I hope this all makes sense so thanx for everyone's help and input.

[Me...]

You should be using water that is filtered, but not heated, to flow into the cell. This would normally be right after the filter. Then you need to find a lower pressure pipe for the water to flow out of the cell into. This could be after the heater but quite often the pressure drop is not enough to ensure good flow all the time.

If you cant find a place in front of the pump, look for the drain fitting on the strainer pot. You should be able to adapt the tubing into that hole.

Probes like to have a nice even pressure and flow. Hopefully the flowcell lines are valved and you can first fully open the "in" valve and then open the "out" valve just until there is adequate flow. You do not want suction in the flowcell. Good flowcells will have a pressure gauge in them so you try to keep a consistent pressure between calibrating and operating.

[Rick Sass]

Thanx for the tip Me about adjusting the outflow valve on the flow cell. I had both valves fully open and I can see know that was not a good idea as the flowcell area for the pH probe was not fully imersed in water, but after adjusting the outflow valve, I know have water in the flowcell at the base of the probe, immersed in pool water.

I have one more related question on Stenner pump sizing. Goldline recomends a pump nop larger than 5 gpd. I ordered a variable speed Stenner pump that outputs no more than 5 gpd with a 1/4" discharge tube. When the pump is on, the discharge is a steady drip and I'm assuming these systems are designed to "maintain" acid level rather than decrease the level from a lower level, that is, there designed to maintain say a 7.6 ph level rather than decrease the level from7.9 to 7.6. Or if this is not correct, should I have gotten a larger discharge pump, say a 10 or 15 gpd model?

[Me...]

Really depends on your acid demand and pool gallonage. I would rather see a small pump run all day than a large one periodically dump a huge load of acid in the pool. I also like to see the acid diluted about 10-1 unless you have high Alkalinity in your fill water.

Stenners or any peristaltic work fine on short distances and they should run a lot or you stand a better chance of crystallization happening which will plug lines and injectors. Diaphragm pumps can be set to have a full stroke and with longer runs you should use small tubing. Why? Because they can pump against high head and the small diameter tubing makes sure there is high velocity to keep everything pumps clean.

In your other thread re: CYA. Keep it at 30 or so. And keep your pH lower rather than higher. Your chlorine will work much better and therefore help you to use less. Trying to save acid by running a higher pH makes for a weaker chlorine and same for higher CYA, it simply ties it up too much. And if your cell needs to have a much higher run time just to maintain a higher free chlorine, not only does your cell life suffer but you will use more acid to keep the pH down.

I really think sometimes that all the hype about CYA in an indoor pool is simply to help slow down any issues seen with runaway chlorine levels. If you have trouble with ORP then your option is TRUE PPM. True as opposed to calculated, which is based off ORP anyways. You can also try to put little current collectors inline on the in/out of your flowcell.

[Rick Sass]

Regarding the Stenner pump output, the pump tube is rated for 5 GPD (#1) and I can get a different pump tube (2) which will output up to 17 GPD with variable speed.The Goldline controller I'm using has a maximum pump time of 2 hours and with the current setup of 5 GPD, I have to reset the controller every 2 hours becuase the unit times out. I'm assuming these systems are designed to "maintain" acid level, say keep it at 7.6, rather than lower the pH level from say 7.9 to 7.5. I thought using a larger pump tube would inject more acid and therefore keep me under the 2 hour runtime of the controller.

Regarding the CYA level, I have an outdoor pool with screened cage in SW FL. I have been reading other forums and the opinion seems to be that for an outdoor pool, ORP is not needed (recommended) because FC does not fluctuate that much and a % of time (no ORP) can be used to control FC with a SWG. Plus, I can have a higher CYA level to buffer UV and sun from lowering the FC levels amd have shorter run times for the SWG.

[Me...]

I'll add something else to my other comments. Your entire pool should be manually balanced to where you want to run it before you calibrate a controller. This includes temperature. And yes, they are meant to maintain a given level. If your overfeed was set to allow enough acid into the pool to adjust it from 7.9 to 7.6 then the potential for overfeeding is always going to be there. And I would head for a level more like 7.4. Chlorine works better and its closer to the pH of your eyes.